1. Field of the Invention
This invention relates to an auto sheet feeder provided in a recording apparatus such as a printer, a copying machine or a facsimile apparatus, and particularly to an auto sheet feeder for automatically separating sheets one by one and feeding them to a recording portion.
2. Related Background Art
In a recording apparatus such as a printer, a copying machine or a facsimile apparatus, besides plain paper, thick paper such as postcards and envelopes and special sheets such as plastic sheets are used as recording sheets. The supply of these recording sheets to the recording apparatus is effected by manually inserting sheets one by one or automatically and continuously feeding sheets by an auto sheet feeder (ASF).
An example of an auto sheet feeder according to the prior art provided in the recording apparatus is shown in FIGS. 7 and 8 of the accompanying drawings. FIG. 7 is a cross-sectional view of an example of the recording apparatus 50 according to the prior art, and FIG. 8 is a front view of an auto sheet feeder 52 provided in this recording apparatus 50.
In FIG. 7, the recording apparatus 50 is provided with a recording portion 53 for recording image information on recording sheets P separated and fed one by one by the auto sheet feeder 52. The recording sheets on which the image information has been recorded in the recording portion 53 are successively discharged from the recording apparatus 50.
The auto sheet feeder 52, as shown in FIGS. 7 and 8, is provided with a pressure plate 55 pivotally provided on a frame 54 and supporting the recording sheets P thereon, feeding rollers 56 for feeding out the recording sheets P supported on the pressure plate 55, a pressure plate spring 58 for biasing the pressure plate 55 toward the feeding rollers 56 and bringing the recording sheets P into pressure contact with the feeding rollers 56, and a separating pawl 59 for separating the recording sheets disposed correspondingly to the corner portion of the leading end of the recording sheets P supported on the pressure plate 55.
The recording sheets P supported on the pressure plate 55 have their opposite side edges regulated by a side reference surface 54a formed on the frame 54 and a movable side guide 60 attached to the pressure plate 55 for movement in the widthwise direction of the recording sheets.
The feeding rollers 56, 56 are cut-away circular rollers having a portion of their outer peripheries cut away, and rollers 57, 57 having a diameter somewhat smaller than the outer diameter of the feeding rollers are provided coaxially with the feeding rollers 56, 56. The pressure plate 55 is designed to be capable of spacing the recording sheets P apart from the feeding rollers 56, 56 against the biasing force of the pressure plate spring 58 by a release cam, not shown.
The operation of the auto sheet feeder 52 of such construction will now be described.
When the feeding rollers 56, 56 are rotated while being in pressure contact with the recording sheets P supported on the pressure plate 55, the recording sheets are separated and fed out one by one by the separating pawl 59. The recording sheet thus fed out has its opposite side edges guided by the side reference surface 54a and the movable side guide 60 and is conveyed toward the recording portion 53 while the skew feeding thereof is suppressed, and is fed into between a conveying roller 61 and a pinch roller 62 provided in the recording portion 53 by a predetermined amount.
At this time, the pressure plate 55 is spaced apart from the feeding rollers 56 by the release cam, not shown, and the feeding rollers 56, 56 are rotated and stopped at a standby position in which the cut-away surfaces thereof become substantially parallel to the recording sheet. In this state, the rollers 57, 57 are rotated with the conveying operation for the recording sheet to thereby mitigate the load during the conveyance of the recording sheet.
In this manner, a recording sheet is fed out and recording is effected in the recording portion 53 without the recording sheet being skewly fed.
In recent years, the downsizing of the recording apparatus has been desired and therewith, the downsizing of the auto sheet feeder has been contrived. When the downsizing of the auto sheet feeder is contrived, it is conceivable to make the portion for supporting the recording sheets small, but the following problems will arise if it is merely downsized.
(1) When the frame 54 is downsized, the length of the side reference surface 54a for guiding one side edge portion of the sheet in the sheet feeding direction becomes short and the skew feeding of the recording sheet occurs or the skew feeding becomes great.
(2) When the movable side guide 60 for regulating the widthwise direction of the recording sheet is made small and thin, the holding force for the recording sheet is weak by only the friction of a molded (resin) part and the regulation of the recording sheet in the widthwise direction thereof cannot be sufficiently accomplished and therefore, the occurrence of the skew feeding of the sheet cannot be suppressed.
(3) When the pressure plate 55 is made small, stress applied to the pressure plate 55 becomes great and the pressure plate is deformed by the occurrence of a creep phenomenon due to long-term preservation. Also, by the pressure plate being small, the surface supporting the recording sheets becomes small and thus, the setting property when the recording sheets are set becomes bad.
Against the occurrence of the above-described skew feeding, it is conceivable to take registration by ramming the recording sheet against the nip portion between the conveying roller 61 and pinch roller 62 stopped to correct skew feeding before the recording operation in the recording portion 53, but when the skew feeding is too great, the skew feeding cannot be sufficiently corrected and moreover, much time is required to take registration and therefore, the evil that the throughput is reduced occurs.
The present invention has been made in view of the above-noted problems and has as its object to provide a compact auto sheet feeder and a compact image forming apparatus in which the skew feeding of sheets is prevented.
The auto sheet feeder of the present invention is provided with:
sheet supporting means provided on the frame of the main body of the apparatus and supporting sheets thereon; and
sheet feeding means for feeding out the sheets supported on said sheet supporting means;
characterized in that a reference surface for regulating one side edge of the sheets fed out by said sheet feeding means is formed on each of said frame and said sheet supporting means.